JP3491044B2 - Method for producing polyolefin-based ultrafine fiber nonwoven fabric - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyolefin-based ultrafine fiber nonwoven fabric, and more particularly, to a method for stably supplying a polyolefin-based ultrafine fiber nonwoven fabric which is particularly excellent for filter applications. . [0002] A thermoplastic resin is heated and melted and then discharged from an orifice of a nozzle. A heating fluid is jetted from the vicinity of an opening end of the orifice to be blown into the flow of the molten resin to be finely divided. A method for forming a group, that is, a method for producing a microfiber nonwoven fabric by a melt blow method is disclosed in JP-B-43-20248, JP-B-44-12848, JP-B-44-13210, and JP-B-44-22.
No. 525, JP-B-44-25870, JP-B-44-25872 and the like. In addition, a polyolefin-based melt blow method is disclosed in
0-46972 and JP-A-54-134177. These methods include at least 1.
A thermoplastic resin having an initial intrinsic viscosity of 4 is thermally degraded from the extruder to the nozzle orifice in the presence or absence of free radicals to reduce the intrinsic viscosity of the polymer in the nozzle orifice to 0. This is a method for producing a melt-blown nonwoven fabric having a melt viscosity of 50 to 300 poise. According to these methods, the thermal degradation of the polymer is remarkable, so that when the molten polymer is spread in the width direction from the extruder to the nozzle, there is a difference in residence time in the width direction. Becomes
As a result, the fabric weight distribution in the width direction of the nonwoven fabric becomes uneven, the distribution of fiber diameters becomes large, or the strength of the nonwoven fabric becomes weak. There is a problem in operation, such as the occurrence of so-called fly, which is scattered in the nozzle, and the opening or closing of the nozzle hole caused by a thermally degraded polymer. In contrast, Japanese Unexamined Patent Publication
In JP-A-3-6107 and JP-A-1-156561, the above-mentioned problems will be solved by using a polyolefin resin having a melt index of 70 to 500 g / 10 min and reducing the melt viscosity at the nozzle orifice to 50 poise or less. And However, according to these methods,
In order to obtain an ultrafine fiber nonwoven fabric having an average fiber diameter of 1.5 μm or less, it must be further thermally degraded,
Since the above problems associated with thermal deterioration, particularly the occurrence of frying, cannot be avoided, the minimum average fiber diameter that can be obtained stably was at most 1.5 μm. Japanese Patent Publication No. 1-60564 discloses a method in which a molecular weight reducing agent is added to a polyolefin having a melt index of 0.1 to 20 g / 10 minutes, and the composition is set so that it is not decomposed in the pelletizing step and decomposes at the spinning temperature. . According to this, it is possible to decompose to an appropriate molecular weight without the problem of poor cutting in the pelletizing process, but because it is a method of decomposing in a line, the degree of decomposition differs depending on the residence time difference at the time of polymer distribution. In addition, the melt viscosity of the polymer becomes uneven, and the weight change rate of the obtained nonwoven fabric increases.
If spinning at a temperature of not less than ℃, the molecular weight reduction effect does not appear, so that there is a problem that frying is unavoidable during the production of ultrafine fiber nonwoven fabric. [0003] The present invention relates to a conventional method for producing a polyolefin-based ultrafine nonwoven fabric,
That is, in order to obtain a nonwoven fabric having a small fiber diameter, it is necessary to lower the melt viscosity of the polymer in the nozzle orifice. For that purpose, it is necessary to reduce the molecular weight of the polymer by thermal deterioration or to increase the nozzle temperature, that is, the polymer temperature. In this case, the weight distribution of the nonwoven fabric in the width direction becomes nonuniform, Distribution becomes large,
Operations such as quality problems such as weakening of non-woven fabric, cut fibers scattered during blowing, so-called frying, blockage of nozzle holes due to thermal degradation of polymer, etc. An object of the present invention is to solve the above problems and to stably supply a polyolefin-based ultrafine fiber nonwoven fabric which is particularly excellent for filter applications. According to the present invention, a thermoplastic resin is heated and melted and then discharged from an orifice of a nozzle, and a heating fluid is injected from the vicinity of an opening end of the orifice to form a flow of the discharged molten resin. In the method of producing an ultrafine fiber nonwoven fabric by spraying and thinning, the thermoplastic resin has a melt index at a temperature of 230 ° C. under a load of 2.160 kg of 500 to 2000 g / 10 minutes and an intrinsic viscosity ([μ] _p ) of 0. A microfiber is spun at a nozzle temperature of 200 to 285 ° C. using a polyolefin resin having a viscosity of 0.5 to 0.9, and the intrinsic viscosity is reduced (Δ [μ] = [μ] _p −).
A method for producing a polyolefin-based ultrafine fiber nonwoven fabric, characterized by producing a nonwoven fabric such that [μ] _f ) is 0.3 or less. Hereinafter, the present invention will be described in detail. The polyolefin-based resin used in the present invention may be a polyolefin-based resin such as polypropylene, polyethylene, or polybutene-1 alone, or a copolymer and / or a blend thereof. The polyolefin resin used in the present invention has a melt index at a temperature of 230 ° C. and a load of 2.160 kg of 500 to 2000 g / min, preferably 1000 to 1500 g / 10 min, and an intrinsic viscosity ([μ] p
) Must be 0.5 to 0.9, preferably 0.6 to 0.8. Melt index is 500g /
If the time is less than 10 minutes, the temperature from the extruder to the nozzle must be increased to adjust the melt viscosity in order to reduce the fiber diameter, so that the process of forming ultrafine fibers after spinning is unstable. Accordingly, scattering of the fiber, which is considered to be caused by the fiber being cut after spinning, so-called fly occurs, or the fiber diameter distribution of the obtained nonwoven fabric is unfavorably increased. If the melt index exceeds 2,000 g / 10 minutes, the melt viscosity becomes too low, so that the distribution of the molten polymer in the nozzle width direction becomes nonuniform. Is too low, and there is a disadvantage that the strength of the nonwoven fabric is too low, causing a problem in practical use. If ([μ] p) is less than 0.5, the molecular weight of the polymer is too low, so that the strength of the nonwoven fabric is reduced,
When the ratio exceeds 0.9, thermal degradation is required as described above, and a problem associated therewith occurs. Further, the intrinsic viscosity ([μ] f) of the fiber after forming the nonwoven fabric is 0.4 to 0.8,
Preferably, it is required to be 0.5 to 0.7.
If ([μ] f) is less than 0.4, the strength of the nonwoven fabric becomes weak, and if it exceeds 0.8, the fiber diameter becomes large, and high performance can be exhibited when used for filter applications. Can not. Furthermore, the intrinsic viscosity decreases (Δ [μ]
= [Μ] p - [μ] f) is 0.3 or less, preferably 0.2 or less. Failure to satisfy this condition
That is, it means that the thermal degradation of the polymer is large between the extruder and the nozzle, and it is not possible to stably produce an ultrafine fiber nonwoven fabric of 1.5 μm or less. The molecular weight distribution of the polyolefin resin is not particularly limited, but is preferably narrow from the viewpoint of spinning stability.
/ Mn is preferably 2 to 5. [0007] The apparatus used in the melt blow method of the present invention comprises:
Although it is based on a well-known thing, in order to suppress the thermal degradation of a polymer, the residence time to the nozzle orifice is preferably within 10 minutes, more preferably within 5 minutes. The temperature of the nozzle is preferably as low as possible within the range where the required fiber diameter can be obtained.
It is preferably 85 ° C. or lower, more preferably 255 ° C. or lower, and still more preferably 250 ° C. or lower. Increasing the nozzle temperature not only promotes thermal degradation of the polymer, but also increases post-spinning instability reduction and leads to the generation of flies. On the other hand, from a practical viewpoint, the temperature is preferably 200 ° C. or higher, more preferably 225 ° C. or higher. As the heating fluid, superheated steam, air, nitrogen gas or the like is suitable. The temperature of the heating fluid is preferably as low as possible within a range sufficient for the thinning of the molten polymer, for the purpose of suppressing an unstable decrease after spinning. For example, in the case of polypropylene, 180 ° C.
It is good to be 400-400 degreeC, More preferably, it is 200-350 degreeC. If the pressure of the heating fluid is too low, the thinning is insufficient, and if it is too high, frying occurs.
It is preferably kg / cm ² . The nonwoven fabric obtained according to the present invention has an extremely small fiber diameter and a sharp distribution among melt blown nonwoven fabrics, and is therefore particularly suitable for filter applications. Further, the nonwoven fabric of the present invention, if necessary, calendering,
Post-processing such as embossing and ultrasonic processing can be performed. In addition, it is electretized by corona discharge,
The collection efficiency as a filter can be increased. The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the present invention. The main characteristic values defined in the text and used in the examples are based on the following methods. Average fiber diameter (μm), fiber diameter variation rate (CV%) A non-woven fabric is photographed by a scanning atomic microscope, and 200 fibers are randomly selected from a 2000-times enlarged photograph, and the diameter is measured. The average fiber diameter was 200 fibers.
The fiber diameter variation rate was determined by the following equation. Fiber diameter variation rate (%) = (δ _n-1 / x) × 100 where δ _n-1 is unbiased dispersion. Nonwoven fabric strength (g / cm) Length and width direction of the nonwoven fabric are 14 cm in length and 2 c in width.
Five samples of m are taken, and a tensile length of 2 cm is cut by elongation with a tensilon, the maximum point stress at that time is determined, and the average value of the five points is converted to a 1 cm width. [0013] Weight per unit variation (CV%) [0013] A sample of 2 cm wide x 10 cm long is taken in the width direction of the nonwoven fabric, each weight is measured, an average value and a standard deviation are obtained, and the unit weight fluctuation is obtained by the following formula. Was. Weight variation (%) = (δ _n-1 / x) × 100 Intrinsic viscosity: [μ] _p , [μ] _f (dl / g) Measured in a tetralin solvent at 135 ° C. [0015] Collection efficiency, pressure drop JIS Z-8901 Dust for test 13 class B method 0.3
It was determined by measuring the dust collection efficiency of a stearic acid aerosol having an average of μm. Example 1 A melt index at a temperature of 230 ° C. and a load of 2.160 kg was 1000 g / 10 min, and ([μ] _p ) was 0.7.
5 polypropylene resin, orifice diameter 0.2m
microfibers using a melt blow method under the conditions of a 0.1 m / min. hole of polypropylene resin, a nozzle temperature of 240 ° C., a traction fluid temperature of 320 ° C., and a traction fluid pressure of 2.5 kg / cm ² using a nozzle of m. A non-woven fabric was manufactured. Table 1 shows the results. The average fiber diameter of the obtained ultrafine fiber nonwoven fabric was 1.0 μm, and the fiber diameter variation rate was 25%. The average basis weight was 30 g / m ² , and the basis weight variation was very uniform at 3.0%.
([Μ] _f ) is 0.55, so (Δ [μ]) is equal to 0.5.
The thermal degradation of the polymer was relatively small. The tensile strength of this ultrafine fiber nonwoven fabric was relatively high, at 450 g / cm. In addition, the spinning state at this time was very stable, and no fly was observed. A continuous operation was carried out for 20 days under these production conditions. However, the operation was still stable after 20 days, and no clogging of the nozzle hole was observed. Furthermore, when the filter characteristics were evaluated using this ultrafine fiber nonwoven fabric, the collection efficiency was 99.6% and the pressure loss was 10 mmH ₂ O, which was very excellent. [Table 1] Examples 2 to 4 and Comparative Examples 1 to 3 Using polypropylene resins having different melt indices and ([μ] _p ), the single hole discharge amount, nozzle temperature, traction fluid temperature and traction fluid pressure were variously changed. Other conditions were the same as in Example 1 to produce a microfiber nonwoven fabric by a melt blow method. Table 1 shows the respective manufacturing conditions and nonwoven fabric characteristics. As is clear from Table 1, Examples 2, 3, and 4 satisfy the conditions of the present invention, whereas Comparative Example 1 has a small melt index and a high nozzle temperature, so that the fiber diameter variation rate (CV%) is high. And the number of flies was large, and continuous operation was impossible for more than three days. In Comparative Example 2, since the melt index was small and the nozzle temperature was not so high, the average fiber diameter was large and the collection efficiency was poor. Comparative Example 3
Has a high melt index, so that the tensile strength of the nonwoven fabric is too low, and the basis weight variation is high, which has a practical problem. According to the production method of the present invention, a nonwoven fabric having a very small fiber diameter and a sharp distribution among meltblown nonwoven fabrics can be obtained without a problem in operation. This melt-blown non-woven fabric makes use of its extra-fine properties,
In particular, it can be used for high performance filter applications.

Continuation of the front page (56) References JP-A-1-234214 (JP, A) JP-A-1-62213 (JP, A) JP-A-2-175694 (JP, A) JP-A-3-80190 (JP) , A) Fully open 1986-148612 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) B29C 33/38, 45/37

Claims (1)

(57) [Claims 1] After heating and melting a thermoplastic resin, the thermoplastic resin is discharged from an orifice of a nozzle, and a heating fluid is jetted from a vicinity of an opening end of the orifice to blow the flow of the discharged molten resin. In the method for producing a microfiber nonwoven fabric by thinning, the thermoplastic resin may be used at a temperature of 230 ° C. under a load of 2.160.
Melt index in kg is 500-2000g
/ 10 minutes, using a polyolefin resin having an intrinsic viscosity ([μ] _p ) of 0.5 to 0.9, and a nozzle temperature of 200 to 2
Spin ultrafine fibers at 85 ° C and reduce intrinsic viscosity (Δ [μ] =
Non- woven fabric so that [μ] _p- [μ] _f ) is 0.3 or less
A method for producing a polyolefin-based ultrafine fiber nonwoven fabric, characterized in that :